Sauropsid: Encyclopedia II - Sauropsid - History of the Term Sauropsida

Sauropsid - History of the Term Sauropsida

The terms Sauropsida ("Lizard Faces") and Theropsida ("Beast Faces") were coined in 1916 by E.S. Goodrich to distinguish between lizards, birds, and their relatives on one hand (Sauropsida) and mammal-like reptiles and mammals (Theropsida) on the other. This division is supported by the nature of the hearts and blood-vessels in each group, and other features such as the structure of the forebrain. According to Goodrich both lineages evolved from an earlier stem group, the Protosauria ("First Lizards") which included some Paleozoic amphibians as well as early reptiles.

In 1956 D.M.S. Watson observed that the first two groups diverged very early in reptilian history, and so he divided Goodrich's Protosauria among them. He also reinterpreted the Sauropsida and Theropsida to exclude birds and mammals respectively.  Sauropsida thus came to refer to the Procolophonia, Eosuchia, Millerosauria, Cheloniana (turtles), Squamata (lizards and snakes), Rhynchocephalia, Crocodilia, Thecodontia, Dinosaurs, Pterosaurs, Ichthyosaurs, and Sauropterygia; while the Theropsida (=Synapsida) included the Pelycosaurs and the Therapsida (mammal-like reptiles).

This classification supplemented, but was never as popular as the classification of the Reptiles (according to Romer's classic Vertebrate Paleontology) into four sub-classes according to the positioning of temporal fenestrae, openings in the sides of the skull behind the eyes. Those divisions are:

• Anapsida - no fenestrae
• Synapsida - one low fenestra (beneath the postorbital and squamosal bones)
• Euryapsida - one high fenestra (above the postorbital and squamosal)
• Diapsida - two fenestrae

All of the above but Synapsida fall under "Sauropsida".

Adapted from the Wikipedia article "History of the Term Sauropsida", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki